Increasingly, the material mix used in trucks and automobiles is changing from low strength, low carbon steel to materials which can, cost-effectively, offer higher specific strength (strength/density). Titanium alloys offer some of the highest specific strengths (strength/density) of all structural alloys, good corrosion and oxidation resistance and good fatigue properties and so should be appealing for automotive applications. But because material and processing costs for titanium-based alloys have not been attractive, titanium and titanium-based alloys and compounds have found only limited application.
Thus, there remains a general need for new practices for manufacturing titanium alloys because they can find applications in automotive vehicles such as, for example, in valves, connecting rods, and springs, and other engine components. The substitution of lower density titanium alloys for ferrous alloys may enable higher maximum engine operating speeds and up to an 8% increase in engine power. Since new electrolytic processes are now becoming available that can offer pure Ti powder at very low cost, there is increasing interest in developing new methods for manufacturing sintered Ti-alloys using these low cost Ti-powders.
Gamma titanium aluminide, γ-TiAl, (as indicated with equal atomic proportions of titanium and aluminum) is a material considered for use in aeronautical applications. It could find automotive applications if it could be processed at acceptable cost levels. It is often prepared in combination with minor proportions of one or more of Nb, Cr, Mn, Mo, Si, Cu, Fe, Sn and V, generally indicated as X, and added for selective enhancement of ductility, corrosion or oxidation resistance or other engineering attributes. But there is a nearly one thousand degree Celsius difference in the melting points of titanium and aluminum. This fact and other processing issues have complicated the preparation of useful article shapes of γ-TiAl—X compositions for automotive applications when using blended elemental powder mixtures of the desired composition.
There is, therefore, a need for an improved method of making titanium alloy articles in general, and there is a particular need for making articles comprising γ-TiAl with relatively minor alloying additions where the individual elemental additions have widely-varying melting points.